1. Field of the Invention
The present invention relates to a filter for a cathode ray tube or other display device and a display device having the filter for a display device on a display panel of a cathode ray tube.
2. Description of the Related Art
As a means for preventing flying glass due to implosion of a cathode ray tube (hereinafter also referred to as a CRT), the technique of adhering a plastic blast prevention film to the surface of the panel glass of the CRT is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 52-87352 and Japanese Unexamined Patent Publication (Kokai) No. 52-87353. By adhering this blast prevention film to the display panel of the CRT, the function of preventing flying glass, which had previously relied only on the panel glass and tension band, can be partially shifted to the blast prevention film. By this, it becomes possible to make the panel glass thinner, which is very effective in practical use with respect to lightening the weight of a CRT and a display device using a CRT.
On the other hand, in a CRT, turning on and off a high drive voltage generates static electricity at the display surface. This attracts surrounding dusts and causes an uncomfortable feeling due to electric shock when touched by the hand. In order to prevent the above problems, as disclosed in for example Japanese Unexamined Patent Publication (Kokai) No. 8-287850, the method of coating an antistatic material on the display panel of the CRT to form an antistatic film to reduce the surface resistance to less than, for example, 109 xcexa9/xe2x96xa1 and connecting to a housing of a ground potential to drain the static electricity is effective.
The antistatic film can be formed by mixing, for example fine particles of tin oxide or ITO or other electrically conductive substances as a filler, into for example a rubber-based, acrylic-based, silicon-based, epoxy-based resin, or other resin, coating the obtained mixture on a film, and causing this to cure by heating, irradiation by ultraviolet rays or irradiation by electron beams etc.
Further, when viewing an object through a transparent material, it is extremely troublesome if the reflected light is strong and there is a clear reflected image. In lenses for eyeglasses, for example, if there is a reflected image called a xe2x80x9cghostxe2x80x9d or xe2x80x9cflarexe2x80x9d, it will give an uncomfortable feeling to the eyes. Further, in a looking glass, there is the problem that the content is not clear due to the light reflected on the glass surface. Problems similar to those described above also occur in CRTs. In order to avoid them, there has been a growing demand for imparting an antireflection function to the display panel of the CRT.
In the related art, in order to prevent the reflection of light causing these problems, the method has been used of adhering an antireflection filter, having an antireflection film formed by covering a substrate with a substance having a different refractive index from that of the substrate by a vacuum deposition process or the like, on the display panel of the CRT. In this case, it has been known that the selection of the thickness of the antireflection film covering the substrate is important in order to raise the antireflection effect the most. When for example the antireflection film is formed by a single layer, it has been known that formation of the antireflection film by using a substance having a lower refractive index than that of the substrate as the material for forming the antireflection film and selecting an optical film thickness of xc2xc of the wavelength of the light being an object of the antireflection, or odd number times thereof, gives the minimum reflection rate, in other words, the maximum transmittance. Here, the xe2x80x9coptical film thicknessxe2x80x9d is given by the product of the refractive index of the material forming the antireflection film and the thickness of the antireflection film. Further, it is possible to form an antireflection film of a multiple layer structure. Some proposals have been made for the selection of the film thickness in this case in for example documents (Optical Technical Contact, Vol. 9, No. 8, p. 17 (1971)).
As the material for forming the above antireflection film, an inorganic oxide or an inorganic halide is mainly used in many cases. They generally have both a low reflection rate and a high transmittance in the visible range.
Summarizing the problems to be solved by the invention, in the CRTs of the related art, however, the transmittance of the display light emitted from the fluorescent surface inside the CRT is adjusted by the panel glass, therefore if the weight is lightened by reduction of the thickness of the panel glass, which becomes possible by adhering the blast prevention film, there is the problem that the transmittance of the display light becomes too high, so the contrast of the displayed image is lowered.
Further, due to the formation of an antireflection film made of inorganic oxide or the like on the display panel of a CRT, there is almost no light absorption at the antireflection film and the reflection at the surface is reduced, therefore an effective transmittance of the display light becomes further higher, so the contrast of the displayed image is degraded in the same way as in the above. In this case, the adjustment of the transmittance to an intended value without a change of the panel glass thickness can be generally easily achieved by changing the material of the panel glass, but according to this method, it becomes necessary to use different glass materials for forming the antireflection film and for not forming the antireflection film, and the glass materials must be frequently changed, which becomes a factor behind a decline in productivity and a rise in the manufacturing costs.
Further, in a CRT having a flat display panel, the mechanical strength fundamentally becomes weak; therefore the thickness of the glass at, for example, the ends of the display panel must be larger than the thickness of the glass of the corresponding portions of a general CRT in order to secure the strength. Due to this, there is the inconvenience that the brightness of text, graphics, and other displayed images is clearly different between the center and the ends of the display panel. From this viewpoint, it is desired to use transparent glass (clear glass) as much as possible for the panel glass material. This also raises the transmittance of the display light.
An object of the present invention is to provide a filter for a CRT or other display device which can prevent a reduction of the contrast of the display screen caused when the panel glass is made thinner by strengthening the mechanical strength of the CRT or when an antireflection film is formed and which can be preferably adhered to even a CRT having a flat display panel and to provide a display device having that filter for a display device on the display panel of a CRT.
To attain the above object, according to a first aspect of the present invention, there is provided a filter for a display device adhered to a display panel of the display device and strengthening a mechanical strength of the display device, comprising a filter substrate and an adhesive layer formed on an adhering surface of the filter substrate to the display panel having a function of adjusting a transmittance of visible light to a predetermined value.
The filter for a display device of the present invention strengthens the mechanical strength of a display device when adhered to the display panel of the display device. Where it is adhered to the display panel of a CRT, the filter for a display device of the present invention strengthens the mechanical strength of the CRT, so it becomes possible to make the panel glass thickness thinner and lighten the weight. Further, if the transmittance of the display light emitted from the fluorescent surface inside the CRT becomes too high by reducing the panel glass thickness, the contrast of the displayed image is lowered, but in the filter for a display device of the present invention, the adhesive layer formed on the surface of the filter substrate adhering with the display panel of the display device has a function of adjusting the transmittance of the visible light to a predetermined value, therefore it becomes possible to properly adjust the transmittance of the display light and suppress the reduction of the contrast of the displayed image.
In the filter for a display device of the present invention, preferably the adhesive layer has a function of adjusting the transmittance of the visible light to a predetermined value by containing at least a dye or a pigment. By adjusting the content of the dye or the pigment, the transmittance of the visible light can be easily adjusted to the predetermined value.
In the filter for a display device of the present invention, preferably an antireflection film is formed on a surface of the filter substrate opposite to the surface of formation of the adhesive layer and further preferably the antireflection film is comprised of a plurality of films. By this, the reflection of light from the display panel of the display device can be suppressed. Further, the adhesive layer formed on the adhering surface with the display panel of the display device can adjust the transmittance of the visible light to the predetermined value, therefore it becomes possible to properly adjust the transmittance of the display light and suppress the reduction of the contrast of the displayed image due to the fact that the effective transmittance of the display light further rises by forming the antireflection film.
In the filter for a display device of the present invention, preferably an antistatic film is formed on a surface of the filter substrate opposite to the surface of formation of the adhesive layer. By this, it further becomes possible to prevent the generation of the static electricity on the display surface of the display device.
Further, to attain the above object, according to a second aspect of the present invention, there is provided a display device comprising a cathode ray tube having at its inside a fluorescent surface emitting light upon being subjected to an electron beam emitted from an electron gun and having a filter for strengthening a mechanical strength of the cathode ray tube adhered to a display panel of the cathode ray tube, wherein an adhering surface of a filter substrate of the filter and the display panel of the cathode ray tube are adhered to each other by an adhesive layer having a function of adjusting the transmittance of visible light to a predetermined value.
In the display device of the present invention, the filter is adhered to the display panel of a cathode ray tube (CRT), whereby the mechanical strength of the CRT is strengthened, so it becomes possible to make the panel glass thinner and thereby realize a reduction of the weight of the display device. Further, if the transmittance of the display light emitted from the fluorescent surface inside the CRT becomes too high by making the panel glass thinner, the contrast of the display device ends up being lowered, but the adhesive layer for adhering the filter and the display panel has the function of adjusting the transmittance of the visible light to a predetermined value, therefore it becomes possible to properly adjust the transmittance of the display light and suppress the reduction of the contrast of the displayed image.
In the display device of the present invention, preferably the display panel of the cathode ray tube is substantially flat. In the case of that the display panel of the CRT is substantially flat, preferably transparent or clear glass is used as much as possible for the panel glass material. Due to this, the transmittance of the display light becomes high, but the adhesive layer for adhering the filter and the display panel has the function of adjusting the transmittance of the visible light to the predetermined value, therefore it easily becomes possible to properly adjust the transmittance of the display light.
In the display device of the present invention, preferably the adhesive layer has the function of adjusting the transmittance of the visible light to a predetermined value by containing at least a dye or a pigment. By adjusting the content of the dye or the pigment, the transmittance of the visible light can be easily adjusted to the predetermined value.
In the display device of the present invention, preferably the antireflection film is formed on a surface of the filter substrate opposite to the surface of formation of the adhesive layer and more preferably the antireflection film is comprised of a plurality of films. By this, the reflection of light from the display panel of the display device can be suppressed. Further, the adhesive layer adjusts the transmittance of the visible light to the predetermined value, so it becomes possible to properly adjust the transmittance of the display light and suppress the reduction of the contrast of the displayed image due to the fact that the effective transmittance of the display light further rises by forming the antireflection film.
In the display device of the present invention, preferably the antistatic film is formed on a surface of the filter substrate opposite to the surface of formation of the adhesive layer. By this, it further becomes possible to prevent the generation of static electricity on the display panel of the display device.